Temperature Measuring Circuit

Abstract

A temperature measuring circuit uses a diode to drain a switched capacitor at two different lengths of time. The capacitor's voltage is amplified, measured, and compared for each length of time to calculate a temperature. The circuitry may cancel out errors due to manufacturing tolerances and variations, as well as offset voltages, supply noise, substrate noise, and other issues. The process may charge a capacitor, then drain the capacitor with a diode for a first period of time, at which point, the diode is switched out of the circuit. The remaining charge in the diode may be amplified, then analyzed using an analog to digital converter. A second measurement may be taken with a different period of time, and the two measurements may be subtracted to yield an absolute temperature.

1 . A temperature measuring circuit configured to:
 charge a capacitor to a steady state charge voltage during a precharge phase;   discharge said capacitor using a diode during a discharge phase to change voltage of said capacitor to a discharge voltage;   halt said discharge phase and amplify said discharge voltage and measure said discharge voltage using an analog to digital converter during a measurement phase;   a controller configured to:
 cause a first precharge phase to be performed; 
 cause a first discharge phase to be performed for a first time period to generate a first discharge voltage; 
 cause a first measurement phase to be performed to generate a first measurement; and 
 calculate a first temperature measurement using said first measurement. 
   
     
     
         2 . The temperature measuring circuit of  claim 1 , said controller further configured to:
 cause a second precharge phase to be performed;   cause a second discharge phase to be performed for a second time period to generate a second discharge voltage;   cause a second measurement phase to be performed to generate a second measurement;   calculate a second temperature measurement based on said first measurement and said second measurement.   
     
     
         3 . The temperature measuring circuit of  claim 1  implemented as part of an integrated circuit. 
     
     
         4 . The temperature measuring circuit of  claim 1 , said second time period being at least ten times said first time period. 
     
     
         5 . The temperature measuring circuit of  claim 1 , said temperature measurement being calculated by a difference in said first measurement and said second measurement. 
     
     
         6 . The temperature measuring circuit of  claim 1  configured to operate continuously. 
     
     
         7 . The temperature measuring circuit of  claim 1  configured to operate on demand. 
     
     
         8 . The temperature measuring circuit of  claim 1  further comprising:
 a second capacitor configured to be charged to said steady state voltage in said second precharge phase; 
 a second diode configured to discharge said second capacitor in said second discharge phase to generate said second discharge voltage. 
 
     
     
         9 . The temperature measuring circuit of  claim 8 , said temperature measurement being calculated in part based on a differential signal between said first discharge voltage and said second discharge voltage. 
     
     
         10 . The temperature measuring circuit of  claim 9 , said first discharge phase and said second discharge phase being performed at least in part simultaneously. 
     
     
         11 . The temperature measuring circuit of  claim 8  wherein said circuit is calibrated by adjusting a length of at least one of said discharge phases. 
     
     
         12 . The temperature measuring circuit of  claim 1  comprising a switched capacitor amplifier. 
     
     
         13 . The temperature measuring circuit of  claim 1 , said first time period and said second time period are fixed time periods. 
     
     
         14 . The temperature measuring circuit of  claim 1 , at least one of said first time period and said second time periods are adjustable time periods. 
     
     
         15 . The temperature measuring circuit of  claim 1 , said diode being a PN junction between a silicon substrate and an N-type well. 
     
     
         16 . The temperature measuring circuit of  claim 1 , wherein amplification of said discharge voltage is performed using a switched-capacitor amplifier. 
     
     
         17 . The temperature measuring circuit of  claim 1  wherein said circuit is calibrated by adjusting the length of said discharge phase. 
     
     
         18 . A method for measuring temperature on a device, said method comprising:
 charging a first capacitor to a steady state charge voltage during a first precharge phase;   discharging said first capacitor using a first diode during a first discharge phase to change voltage of said first capacitor to a first discharge voltage;   halt said first discharge phase and amplify said first discharge voltage and measure said first discharge voltage using an analog to digital converter during a first measurement phase;   charging a second capacitor to a steady state charge voltage during a second precharge phase;   discharging said second capacitor using a second diode during a second discharge phase to change voltage of said second capacitor to a second discharge voltage;   halt said second discharge phase and amplify said second discharge voltage and measure said second discharge voltage using an analog to digital converter during a second measurement determining a temperature based on a difference between said first discharge voltage and said second discharge voltage.   
     
     
         19 . The method of  claim 18 , said first capacitor and said second capacitor are the same capacitor. 
     
     
         20 . The method of  claim 19 , said first diode and said second diode are the same diode. 
     
     
         21 . The method of  claim 21  being performed when all circuit components are on the same integrated circuit. 
     
     
         22 . The method of  claim 18  further comprising:
 charging said second capacitor to a steady state charge voltage during a third precharge phase; 
 discharging said second capacitor using said second diode during a third discharge phase to change voltage of said second capacitor to a third discharge voltage; 
 halt said third discharge phase and amplify said third discharge voltage and measure said third discharge voltage using said analog to digital converter during a third measurement phase; 
 determining a second temperature based on at least said first discharge voltage, said second discharge voltage, and said third discharge voltage. 
 
     
     
         24 . The method of  claim 18 , said first diode and said second diode are matched diodes. 
     
     
         25 . The method of  claim 18 , said first capacitor and said second capacitor are matched capacitors. 
     
     
         26 . The method of  claim 18 , amplification of said discharge voltages being performed using a differential switched-capacitor amplifier.